Thermal processing torches, such as plasma arc torches, are widely used in the heating, cutting, gouging and marking of materials. A plasma arc torch generally includes an electrode, a nozzle having a central exit orifice mounted within a torch body, electrical connections, passages for cooling, and passages for arc control fluids (e.g., plasma gas). Optionally, a swirl ring is employed to control fluid flow patterns in the plasma chamber formed between the electrode and the nozzle. In some torches, a retaining cap can be used to maintain the nozzle and/or swirl ring in the plasma arc torch. In operation, the torch produces a plasma arc, which is a constricted jet of an ionized gas with high temperature and sufficient momentum to assist with removal of molten metal.
A manually operated thermal processing torch, such as a handheld torch with a trigger switch for starting a cutting arc, can include multiple consumable parts. In addition, a manual torch can include protection circuitry that outputs power to enable torch operations only after it senses the presence of the consumables. For example, a handheld torch can have a consumable sense circuit configured to prevent accidental trigger activation that may involve application of a high open-circuit voltage to an operator while the operator is changing the consumables. A traditional consumable sense circuit typically detects the presence of at least one consumable in a torch via physical contact, such as when the consumable depresses a plunger or switch associated with the sense circuit as the consumable is being installed into the torch. Similarly, an automated/mechanized plasma arc torch, which can operate with minimal user intervention, can include multiple consumable components and consumable sense circuitry that detects the presence of at least one consumable in a torch via physical contact.
FIG. 22 shows an exemplary prior art consumable detection circuit diagram that uses physical contact between the consumable and a component of the detection circuit to perform consumable detection. As shown, the detection circuit 2200 can be incorporated into a plasma arc torch 2204. The detection circuit 2200 includes a sense switch 2202 (e.g. a momentary on-off switch), such as in the form of a plunger that is adapted to complete the switch 2202 when the plunger is depressed. In operation, as a consumable 2206 is attached to the torch 2204, the consumable 2206 is adapted to physically depress the plunger to close the sense switch 2202, which results in the transmission of a consumable-sense signal 2208 from the detection circuit 2202 to the torch 2204. The torch 2204 also includes a trigger switch 2210 configured to generate a start signal 2212 for initiating power to enable torch operations when the trigger switch 2210 is closed. As shown, the trigger switch 2210 is electrically interlocked to the sense switch 2202 in such a way that the trigger switch 2210 is not closed unless the sense switch 2202 is closed. Hence, the consumable sense signal 2208 is necessary to complete the trigger switch circuit 2210 to generate the start signal 2212.
FIG. 23 shows another exemplary prior art consumable detection circuit diagram that employs a physical-contact based approach for consumable detection. The detection circuit 2300 can be substantially similar to the detection circuit 2200 without the electrical interlocking function. In operation, when a consumable 2306 is attached to the torch 2304, the consumable 2306 physically contacts a component of the detection circuit 2300 and closes the sense switch 2302, in which case a consumable-sense signal 2308 is transmitted from the detection circuit 2300 to the torch 2304. The torch 2304 also includes a trigger switch 2310 configured to generate a start signal 2312 for initiating power to enable torch operations when the trigger switch 2310 is closed. Similar to the detection circuit 2200, the consumable-sense signal 2308 is separated from the start signal 2312, but in the detection circuit 2300 the sense switch 2302 is not interlocked to the trigger switch 2310 such that the consumable sense signal 2308 is not necessary to complete the trigger switch circuit 2310 (as is required in the detection circuit 2200).
In many scenarios, physical-contact based detection approaches may not be sufficiently robust to prevent accidental firing and/or trigger activation. In mechanized torches where many functions are automated and torch operations are performed with minimal human intervention, a more automated approach for detecting the installation of consumables is desired.